macOS: Add support for dead keys

I have modified GLFW to support dead keys on macOS. That was painful.
Fixes #465

glfw/cocoa_init.m

@@ -208,6 +208,9 @@ static GLFWbool updateUnicodeDataNS(void)
         _glfw.ns.unicodeData = nil;
     }
 
+    for (_GLFWwindow *window = _glfw.windowListHead;  window;  window = window->next)
+        window->ns.deadKeyState = 0;
+
     _glfw.ns.inputSource = TISCopyCurrentKeyboardLayoutInputSource();
     if (!_glfw.ns.inputSource)
     {

glfw/cocoa_platform.h

@@ -101,6 +101,8 @@ typedef struct _GLFWwindowNS
 
     // The text input filter callback
     GLFWcocoatextinputfilterfun textInputFilterCallback;
+    // Dead key state
+    UInt32 deadKeyState;
 } _GLFWwindowNS;
 
 // Cocoa-specific global data

glfw/cocoa_window.m

@@ -719,20 +719,98 @@ static const NSRange kEmptyRange = { NSNotFound, 0 };
     [super updateTrackingAreas];
 }
 
+static inline UInt32
+convert_cocoa_to_carbon_modifiers(NSUInteger flags) {
+    UInt32 mods = 0;
+    if (flags & NSEventModifierFlagShift)
+        mods |= shiftKey;
+    if (flags & NSEventModifierFlagControl)
+        mods |= controlKey;
+    if (flags & NSEventModifierFlagOption)
+        mods |= optionKey;
+    if (flags & NSEventModifierFlagCommand)
+        mods |= cmdKey;
+    if (flags & NSEventModifierFlagCapsLock)
+        mods |= alphaLock;
+
+    return (mods >> 8) & 0xFF;
+}
+
+static inline void
+convert_utf16_to_utf8(UniChar *src, UniCharCount src_length, char *dest, size_t dest_sz) {
+    CFStringRef string = CFStringCreateWithCharactersNoCopy(kCFAllocatorDefault,
+                                                            src,
+                                                            src_length,
+                                                            kCFAllocatorNull);
+    CFStringGetCString(string,
+                       dest,
+                       dest_sz,
+                       kCFStringEncodingUTF8);
+    CFRelease(string);
+}
+
+static inline GLFWbool
+is_ascii_control_char(char x) {
+    return x == 0 || (1 <= x && x <= 31) || x == 127;
+}
+
 - (void)keyDown:(NSEvent *)event
 {
     const unsigned int scancode = [event keyCode];
+    const NSUInteger flags = [event modifierFlags];
+    const int mods = translateFlags(flags);
     const int key = translateKey(scancode, GLFW_TRUE);
-    const int mods = translateFlags([event modifierFlags]);
+    const GLFWbool process_text = !window->ns.textInputFilterCallback || window->ns.textInputFilterCallback(key, mods, scancode) != 1;
     _glfw.ns.text[0] = 0;
-    if (!window->ns.textInputFilterCallback || window->ns.textInputFilterCallback(key, mods, scancode) != 1) {
+    if (!_glfw.ns.unicodeData) {
+        // Using the cocoa API for key handling is disabled, as there is no
+        // reliable way to handle dead keys using it. Only use it if the
+        // keyboard unicode data is not available.
+        if (process_text) {
             // this will call insertText with the text for this event, if any
             [self interpretKeyEvents:[NSArray arrayWithObject:event]];
-        if ((1 <= _glfw.ns.text[0] && _glfw.ns.text[0] <= 31) || (unsigned)_glfw.ns.text[0] == 127) _glfw.ns.text[0] = 0;  // dont send text for ascii control codes
+        }
+    } else {
+        static UniChar text[256];
+        UniCharCount char_count = 0;
+        if (UCKeyTranslate(
+                    [(NSData*) _glfw.ns.unicodeData bytes],
+                    scancode,
+                    kUCKeyActionDown,
+                    convert_cocoa_to_carbon_modifiers(flags),
+                    LMGetKbdType(),
+                    (process_text ? 0 : kUCKeyTranslateNoDeadKeysMask),
+                    &(window->ns.deadKeyState),
+                    sizeof(text)/sizeof(text[0]),
+                    &char_count,
+                    text
+                    ) != noErr) {
+            debug_key(@"UCKeyTranslate failed for scancode: 0x%x (%s) %s\n", scancode, safe_name_for_scancode(scancode), format_mods(mods));
+            window->ns.deadKeyState = 0;
+            return;
+        }
+        if (process_text) {
+            // We check if cocoa wants to insert text, as UCKeyTranslate
+            // inserts text even when the cmd key is pressed. For instance,
+            // cmd+a will result in the text a.
+            [self interpretKeyEvents:[NSArray arrayWithObject:event]];
+            debug_key(@"char_count: %lu cocoa text: %s\n", char_count, format_text(_glfw.ns.text));
+            GLFWbool cocoa_wants_to_insert_text = !is_ascii_control_char(_glfw.ns.text[0]);
+            _glfw.ns.text[0] = 0;
+            if (char_count && cocoa_wants_to_insert_text) convert_utf16_to_utf8(text, char_count, _glfw.ns.text, sizeof(_glfw.ns.text));
+        } else {
+            window->ns.deadKeyState = 0;
+        }
+        if (window->ns.deadKeyState && char_count == 0) {
+            debug_key(@"Ignoring dead key. deadKeyState: 0x%x scancode: 0x%x (%s) %s\n",
+                    window->ns.deadKeyState, scancode, safe_name_for_scancode(scancode), format_mods(mods));
+            return;
+        }
     }
     debug_key(@"scancode: 0x%x (%s) %stext: %s glfw_key: %s\n",
             scancode, safe_name_for_scancode(scancode), format_mods(mods),
             format_text(_glfw.ns.text), _glfwGetKeyName(key));
+    if (is_ascii_control_char(_glfw.ns.text[0])) _glfw.ns.text[0] = 0;  // dont send text for ascii control codes
     _glfwInputKeyboard(window, key, scancode, GLFW_PRESS, mods, _glfw.ns.text, 0);
 }
 
@@ -1235,6 +1313,7 @@ int _glfwPlatformCreateWindow(_GLFWwindow* window,
                               const _GLFWctxconfig* ctxconfig,
                               const _GLFWfbconfig* fbconfig)
 {
+    window->ns.deadKeyState = 0;
     if (!initializeAppKit())
         return GLFW_FALSE;
 
@@ -1779,16 +1858,7 @@ const char* _glfwPlatformGetScancodeName(int scancode)
     if (!characterCount)
         return NULL;
 
-    CFStringRef string = CFStringCreateWithCharactersNoCopy(kCFAllocatorDefault,
+    convert_utf16_to_utf8(characters, characterCount, _glfw.ns.keyName, sizeof(_glfw.ns.keyName));
-                                                            characters,
-                                                            characterCount,
-                                                            kCFAllocatorNull);
-    CFStringGetCString(string,
-                       _glfw.ns.keyName,
-                       sizeof(_glfw.ns.keyName),
-                       kCFStringEncodingUTF8);
-    CFRelease(string);
-
     return _glfw.ns.keyName;
 }